1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for conditioning a conductive polishing pad.
2. Description of the Related Art
Electrochemical Mechanical Processing (Ecmp) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion as compared to conventional Chemical Mechanical Polishing (CMP) processes. Ecmp systems may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias applied between the substrate and an electrode. Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. The bias may be applied to the substrate surface by a conductive contact disposed on or through a polishing material upon which the substrate is processed. The polishing material may be, for example, a conductive polishing pad disposed on a platen. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the polishing material that enhances the removal of the conductive material from the substrate.
The conductive polishing pad is an important aspect of the Ecmp process. The conductive polishing pad must have the appropriate mechanical properties for substrate planarization while minimizing the generation of defects in the substrate during polishing. Such defects may be scratches in the substrate surface caused by raised areas of the pad or by polishing by-products disposed on the surface of the pad, such as abraded portions of the pad, agglomerations of abrasive particles from a polishing slurry, removed materials from the substrate, and the like. The conductive polishing pad generally deteriorates naturally during polishing due to wear and/or accumulation of polishing by-products on the pad surface. Thus, the pad surface must periodically be refreshed, or conditioned to restore the performance of the pad.
Conventionally, an abrasive conditioning disk is used to work the top layer of the pad surface into a state that possesses desirable polishing results. However, mechanical conditioning has an adverse affect on the pad lifetime. Additionally, abrasive particles which may come free from the conditioning disk during conditioning contribute to scratches and defect generation on the substrate surface. Some conductive polishing pads withstand conditioning by abrasion relatively well. However, other conductive polishing pads are much more sensitive to conditioning by abrasion due to their low thickness or fragility. Conditioning these pads by abrasion may damage the pad and/or may severely reduce the pad lifetime, adding to the time and cost of production.
Another factor affecting the usable life of conductive polishing pads is the formation of oxides on the conductive pad surface, for example, the formation of tin oxide on the surface of a pad containing tin metal. Also affecting the usable life of conductive polishing pads is conductive material by-product contamination, such as tungsten and copper by-products, from conductive material polishing processes. During Ecmp of conductive materials, copper by-products will precipitate out of the electrolyte solution. The precipitates will then contaminate the polishing pad as well as other areas of the polishing tool, including the polishing head, the platen, the conditioning head, among others. This precipitate does not dissolve in de-ionized water (DI water) and makes operation and maintenance of the polishing pad and tool difficult.
Therefore, there is a need for an improved method for conditioning conductive polishing pads.